It’s a sight few visitors to northern California’s coastal waters will ever forget: kelp – giant seaweed if you prefer – growing in lush underwater forests that provide essential habitat for a multitude of species such as rockfish, crabs, mollusks, and even marine mammals like sea otters.

But now a troubling question arises: What does the future hold for these iconic kelp forests and the rich marine life of the Monterey Peninsula and other areas? (Scroll down for a slideshow of images by professional underwater photographer Brandon Cole.)

Few sizable patches of bull kelp remain along some 200 miles of California coastline in Mendocino and Sonoma counties. Satellite images portray a loss of more than 95% over just the past seven years or so. In Monterey and Carmel bays, both bull kelp and giant kelp species are suffering. An underwater heatwave is partly responsible, depleting nutrients in the water and making it more difficult for young kelp plants to recruit and for adults to flourish. Contributing to the perfect storm are purple sea urchins, with their insatiable appetites for the kelp. 

Added to the troubling satellite views of the declining kelp forests on coastal ocean surfaces are the extraordinary underwater views few other than marine photographers have documented. That’s where the vivid images taken by Brandon Cole come in. Cole has been scuba diving in the area since the 1980s, but it’s what he’s seeing more recently that has him “very worried.” And with good reason. 

With the decline of sea stars as a result of a wasting disease fueled by warming ocean temperatures, gorgeous but voracious purple sea urchin populations have grown rapidly … and largely unchecked. Given a penchant for cool, nutrient-rich waters, even those kelp plants surviving the onslaught of hungry sea urchins are struggling as a result of climate change. Fishes and invertebrates depending on kelp and the kelp forest for food and shelter are undernourished and at risk.  So much so that northern California’s culturally important and once historically robust abalone fisheries have been shut down.  

Humans, plants, and animals, all closely tied to each other, now find themselves confronting an ecosystem sadly out of balance. A selection from among thousands of Brandon Cole’s underwater images tells the story in ways written words simply cannot. Scroll forward and backward to see each image and its corresponding caption details. Take a look. 

Photo details:

Learn more about each photo by matching the number on the short photo caption to the more detailed description below.

Photo one: Giant kelp (Macrocystis pyrifera) is the ocean’s largest plant, a seaweed of superlatives. This brown algae can reach nearly 200 feet in height. When sea conditions are optimal, it can grow up to two feet in a single day.

Photo two: Blue rockfish are just one of many fish species scuba divers encounter white exploring the California’s Monterey Bay National Marine Sanctuary. Healthy kelp forests support healthy fish stocks.

Photo three: Kelp forests provide critical habitat for hundreds of species of invertebrates. Here we see a northern kelp crab, a fish-eating sea anemone, and a purple-ringed topsnail.

Photo four: A 12-inch-long giant kelpfish, master of camouflage, shelters amongst the tangle of leaf-like blades. It feeds on crustaceans, molluscs, and small fish. Many of these animals feed directly on kelp or on smaller plants and animals living on kelp.

Photo five: A southern sea otter lounges in Monterey Bay. Otters feed on the wealth of invertebrate life resident in kelp beds. They also wrap themselves up in the floating fronds to keep from drifting away when it’s time to nap or groom themselves.

Photo six: An aerial photograph looking down on the canopy of giant kelp plants in Carmel Bay on the Monterey Peninsula. Some rocky coastal reefs still have thick forests of kelp, while others have lost their coverage completely. Warmer than average sea water temperatures in recent years have negatively impacted kelp growth and recruitment.

Photo seven: The kelp forest under siege. An army of ravenous purple sea urchins (Stronglyocentrotus purpuratus) attacks 100-foot-tall trees of giant kelp, starting at the root-like holdfast structure that anchors the towering plants to the seafloor.

Photo eight: Purple sea urchin densities of more than 500 times normal have been measured in the Monterey area, and some 1500 times greater than normal near Mendocino farther up the coast.

Photo nine: A diver conducting a survey of the marine life at Chase Reef in Monterey Bay finds sea urchins grazing at the base of a few bull kelp (Nereocystis luetkeana) plants attached to granite boulders covered with orange tunicates.

Photo ten: Sunflower sea stars are urchin-eating-machines. This picture was taken 20 years ago, when these important predators were common. In the nearly 80 scuba dives Cole did in year 2020 while documenting the kelp-urchin crisis in central and northern California, he did not see a single sunflower star.

Photo eleven: The Sea Star Wasting Disease (SSWD) that began in 2013 has affected more than 20 species of sea stars. Warm water events and a virus are thought to be responsible for SSWD, which usually kills the animal. They literally disintegrate and turn into a pile of goo. The near total extermination of sunflower stars along the California coast removed a top urchin predator from the ecosystem, contributing to the explosion in sea urchin numbers.

Photo twelve: This rocky reef used to be covered in thick kelp growth. Now it is an urchin barrens. In such high densities, purple sea urchins consume every adult kelp plant. Newly recruited kelps don’t stand a chance either. As soon as they settle, the juvenile plants are eaten by the waiting urchins.

Photo thirteen: Red sea urchins (the larger ones at top) join purple urchins in feasting on kelp. Though both species feed on bull and giant brown algaes as well as smaller plant species carpeting the reef, the purple urchin population is responsible for most of the devastation in central and northern California.

Photo fourteen: Robbed of their main food, red abalone are starving. Their numbers have decreased dramatically along California’s north coast, more evidence of the interconnectedness of this marine ecosystem. Here an abalone searches in vain for kelp amongst a barren landscape dominated by sea urchins.

Photo fifteen: One of the few sizeable stands of bull kelp remaining along the Mendocino coast, just offshore Portuguese Bay.

Photo sixteen: A lone blue rockfish swims past the graceful sweep of the blades of a bull kelp plant. The large air-filled sphere at right called a pneumatocyst buoys up the entire plant. Fish abundance and diversity have declined noticeably in areas where kelp once thrived.

Photo seventeen: What does the future hold for California’s enchanting and imperiled undersea kelp forests?

Also see: Ninety-five percent of bull kelp forests have vanished from 200-mile stretch of California coast

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Bud Ward

Bud Ward was editor of Yale Climate Connections from 2007-2022. He started his environmental journalism career in 1974. He later served as assistant director of the U.S. Congress's National Commission...